1. Field of the Invention
This invention relates to holographic interferometry and more particularly to a method and apparatus for testing an aligning an optical system wherein the system under test is interrogated by a wavefront produced by a hologram and the wavefront returning from the system under test is compared to a reference wavefront which is also produced by the hologram.
2. Description of the Prior Art
Interferometry is a process wherein a light wavefront from a test object or system is interfered with a reference wavefront to produce a fringe pattern indicating differences of the test wavefront from the reference wavefront. Examples of interferometers include those described by Michelson, Twyman, Greene, Mach, Zender, and Fizeau.
Holography is a process by which the amplitude and phase variation across the wavefront from an object can be recorded photographically and subsequently reproduced. The photographic record of the wavefront is referred to as a hologram and the wavefront reproduced from the hologram is said to have been reconstructed.
Holographic interferometry has been performed using a holographically reconstructed wavefront as the interferometric reference wavefront. Examples of prior art holographic interferometric techniques are described in Optical Shop Testing, Chapter 12 by J. C. Wyant, pgs. 381-389; U.S. Pat. No. 3,672,776 issued to R. E. Brooks entitled "Holographic Real-Time Interferometry With a Reconstructed Reference Beam"; U.S. Pat. No. 4,396,289 issued to S. D. Fantone entitled "Method and Apparatus for Holographic Testing of Optical Components".
In all the above techniques, additional means are required to produce the proper wavefront needed to interrogate the system under test. Specifically, a lens is used to generate the proper vergence and a beamsplitter is used to combine the test and reference beams. These additional means result in added complexity and cost.